Rapid Chemical Enrichment by Intermittent Star Formation in GN-z11

Abstract

We interpret the peculiar supersolar nitrogen abundance recently reported by the James Webb Space Telescope observations for GN-z11 ( z = 10.6) using our state-of-the-art chemical evolution models. The observed CNO ratios can be successfully reproduced—independently of the adopted initial mass function, nucleosynthesis yields, and presence of supermassive (>1000 M ⊙ ) stars—if the galaxy has undergone an intermittent star formation history with a quiescent phase lasting ∼100 Myr, separating two strong starbursts. Immediately after the second burst, Wolf–Rayet stars (up to 120 M ⊙ ) become the dominant enrichment source, also temporarily (<1 Myr) enhancing particular elements (N, F, Na, and Al) and isotopes ( 13 C and 18 O). Alternative explanations involving (i) single burst models, also including very massive stars and/or pair-instability supernovae, or (ii) pre-enrichment scenarios fail to match the data. Feedback-regulated, intermittent star formation might be common in early systems. Elemental abundances can be used to test this hypothesis and to get new insights on nuclear and stellar astrophysics.